<div class="btn-group" role="group" aria-label="...">
  <button type="button" class="btn btn-default" data-bind="visible:btnSmallVisible">small</button>
  <button type="button" class="btn btn-default" data-bind="visible:btnMiddleVisible">middle</button>
  <button type="button" class="btn btn-default" data-bind="visible:btnSmallVisible">large</button>
</div>